Check valves are used in piping systems to allow the flow of a fluid (a liquid, slurry, or gas) in one direction but not in the other direction. A ball-type check valve utilizes a ball which is not directly attached to any other component of the valve, but which is constrained within a cage or other supporting assembly. When the fluid flows in the allowed direction, the ball is supported on a device (such as a retainer cup with orifices around the periphery) which allows fluid to flow around the perimeter of the ball. When the fluid flows in the opposite direction, the ball is pressed against a constricted passageway called a "seat", which blocks the flow in that direction.
Various ball-type check valves have been developed for conventional fluid-handling systems. See, e.g., U.S. Pat. Nos. 4,091,849 (Stevenson 1978), 2,328,014 (Heigis 1941), 4,236,759 (Lysenko 1980) and 2,279,513 (Hage 1939).
More sophisticated ball-type check valves have been developed for use in oil and gas drilling and workovers, which involve high pressures, high temperatures, and abrasive fluids such as drilling muds and cements. Those check valves have several distinct uses. For example, the ball-type check valves disclosed in U.S. Pat. No. 3,474,861 (Watkins 1968) and in U.K. patent application GB-2-102-474-A (Cunningham et al) are designed as blowout preventers. Some degree of flow in the upward direction is allowed, but if the upward flow exceeds a certain rate, it will carry the ball up to the seat and stop the flow. By contrast, valves used in "float" equipment during oil and gas drilling are designed to stop any upward flow. They are used during operations such as cementing a string of casing inside a wellbore during a drilling operation, or closing off a depleted formation during a workover. Such valves are described in U.S. Pat. Nos. 1,882,314 (Burt 1932), 3,776,258 (Dockins 1973), and 4,655,247 (Westra et al, 1987).
As used herein, "oil and gas drilling operations" includes any operations (such as cementing, workovers, etc.) that are done to create wells (including production or injection wells) that are involved in producing oil and/or gas.
U.S. Pat. No. 4,655,247 relates to a ball-type check valve sold by Gemoco of Houma, La. (a division of Chromalloy Company, which is a subsidiary of Sequa Corporation), which is widely used within the oil and gas industry. The design of these valves can be appreciated by considering the operating conditions they must endure. For example, a proposed American Petroleum Institute recommended procedure for testing float equipment requires that valves designed for use in cementing operations be tested by pumping drilling mud carrying 2 to 4% sand through the valve at rates of 10 barrels per minute (for any valve in casing sizes of 4.5 inches or larger) or 6 bbl/min (for smaller casing and tubing sizes). After being abraded in that manner for 24 hours, the valves must withstand 5000 pounds per square inch (psi) of back pressure.
The ball-type check valve described in U.S. Pat. No. 4,655,247 contains a flexible skirt near the outlet, which serves several purposes. As downward flow through the valve begins, the skirt serves as a restriction which reduces the area of the peripheral channels. This causes most of the fluid to flow initially through the interior passageway (i.e., through the retainer cup), which promotes rapid settling of the ball on the retainer cup and reduces hammering. After the ball settles on the retainer cup, the fluid must flow through the peripheral channels, which causes the flexible skirt to flex inward. This allows high volumes of drilling mud or cement and large particles to pass through the peripheral channels. In addition, the flexible skirt helps to create a zone of low pressure below the ball, which helps keep the ball securely settled on the cup during downward flow. When the pressure is reversed and upward flow begins, the skirt flexes outward and directs most of the fluid into the interior passage, which ensures that the ball will be lifted off the retainer cup and seated promptly to block the inlet with minimal hammering.
Despite those advantages, the flexible skirt configuration has several limitations. Most importantly, it is difficult to use a flexible skirt in a valve in small casing or tubing (4" diameter or less). The flexible skirt also increases the manufacturing cost; since it cannot be manufactured out of the same metal or hard plastic used to make the rest of the valve, each piece must be fabricated separately, then the components must be assembled.
One object of the present invention is to create a ball-type check valve which can operate under conditions of high pressure, high temperature, and abrasion, but which eliminates the need for the flexible skirt disclosed in U.S. Pat. No. 4,655,247. A second object of the present invention is to create a ball-type check valve for oil and gas drilling, which is small enough to be fitted into casing or tubing with a diameter of 4" or less.
Another object of this invention is to create a ball-type check valve capable of withstanding harsh conditions, which can be constructed from a minimal number of components. A fourth object is to create a check valve for use in oil and gas drilling, which can be assembled from a minimum number of components using a standard collar or shoe as the cage that holds the valve assembly.